A hybrid vehicle (“HEV”) uses multiple propulsion systems to provide motive power. The most commonly available HEV is a gasoline-electric hybrid vehicle, which uses gasoline to power an internal-combustion engine (“ICE”) and rechargeable batteries to power an electric motor. A full hybrid, sometimes also called a strong hybrid, is a vehicle that can run on just the engine, just the batteries, or a combination of both.
Mass-produced full hybrid HEVs, such as the Toyota Prius, currently recharge their batteries by capturing kinetic energy via regenerative braking and, more predominantly, by using the ICE to run the electric motor as a generator during periods of cruising or idling to produce battery-charging current. By contrast, wholly electric vehicles use batteries charged by an external source such as the grid or a generator mounted on a towed trailer.
Nearly all commercially available hybrids use gasoline as the fuel for the ICE, although some HEVs have been built which use diesel, ethanol, plant-based oils (“biofuels”) and the like. HEVs have been developed primarily to lessen dependency on petroleum-based fuel and to minimize the emission of pollutants and greenhouse gases while maintaining a level of performance acceptable to the purchasing public. HEVs have accomplished this to a significant degree, achieving mileages of 50-70 mpg.
A full hybrid, sometimes also called a “strong hybrid”, is a vehicle that can run on just the engine, just the batteries, or a combination of both. As is known to those of ordinary skill in the art, the differing “torque vs. RPM” characteristics of the internal combustion and electrical motors operate synergistically; an internal combustion engine's torque is minimal at lower RPMs, since the engine must be its own air pump. Thus, the need for reasonably rapid acceleration from a standing start results in an engine which is much larger than required for steady speed cruising. On the other hand, an electrical motor exhibits maximum torque at stall; therefore this engine is well suited to complement the internal combustion engine's torque deficiency at low RPMs, allowing the use of a much smaller and therefore more fuel efficient engine.
A smaller, less flexible ICE may accordingly be used that is designed for maximum efficiency, often using variations of the conventional Otto cycle, such as the Miller or Atkinson cycle that contribute significantly to the higher overall efficiency of the vehicle, with regenerative braking playing a much smaller role. A computer oversees operation of the entire system, determining which of the ICE and electric motor should be running, or if both should be in use (e.g., for short bursts additional power or for battery charging), shutting off the ICE when the electric motor is sufficient to provide the power.
While less emissive and more energy-efficient than HEVs, battery electric vehicles have been held back by perceived range limitations, charge-time requirements and battery expense. Ranges of 100-200 miles per charge are currently obtainable, but the public perceives that it needs greater range despite studies showing that most commuters drive less than 50 miles per day. Charge times (0-100%) of 5-7 hours are unattractive to the public, which has yet to appreciate that charge time is not critical when charging is performed overnight. Battery expense remains a challenge, but is primarily a consequence of a lack of mass production of the battery chemistries having the best fit for BEV use.
Research and development activity has accordingly been directed by some into a class of vehicles commonly referred to as “plug-in hybrid electric vehicles” (“PHEVs”). The current focus of attention of hobbyists and, perhaps, one or more members of the auto industry, PHEVs are HEVs whose batteries can be recharged from the electrical power grid and which can accordingly provide a limited “electric-only” range without the use of the ICE. The PHEV can accordingly be ICE-independent (e.g., gasoline-independent) at moderate speeds for daily commuting, and yet have the extended range of a hybrid for long trips, thereby producing even less fewer emissions than an HEV.
The degree of environmental benefit from a PHEV depends, of course, on the source of the electrical power. Electricity generated by wind, solar, and/or other renewable sources will be cleaner than electricity generated with coal, the most polluting source, for example. Electricity generated with coal in a central power plant, however, is still much cleaner than pure gasoline propulsion, due to the much greater efficiencies of a central plant, and the relatively easier monitoring and upgrading of pollution-control measures at stationary sources. Since the range of a PHEV is not limited by battery capacity, it should be more publicly acceptable than a pure EV. Since it is only preferable, but not necessary, that it be plugged into the grid, charge times are not at issue either. It should be understood, incidentally, that the term “grid” includes such local sources of electricity as rooftop solar or other local renewable sources such as windmills, fuel cells and the like. All sources of charging current that are external to the vehicle are within the scope of the term “grid” as used herein.
Similarly, the invention herein is not dependant on the particular cycle or particular fuel of the ICE. Similarly, it is known that the ICE can be fueled by diesel, plant-derived fuels, synthetic fuels, hydrogen, mixtures of some of the foregoing and so forth. It can use an Otto cycle, Miller cycle, Atkinson cycle, or any other desired cycle. All are within the scope of this invention.
Lastly, it should be recognized that this invention is not limited to HEVs using an ICE. As will be clear, a vehicle using an external combustion engine, fuel cell or other source of motive power that relies on non-grid fuel are within the scope of the invention.
While HEVs are being offered to the public in increasing numbers, there are currently no PHEVs available despite the clear advantages of a PHEV.